1. Field of the Invention
This invention pertains to apparatus and methods for sorting transparent plastic articles such as plastic bottles for recycling, and more particularly to methods of identifying the composition of bottles and sorting the bottles for recycling.
2. Description of the Related Art
The marketability of presorted plastic bottles is significantly greater than the marketability of unsorted plastic bottles. Thus, it is advantageous to sort plastic bottles for recycling into marketable categories. Sortation of plastic beverage and household containers has been performed manually, which is a labor intensive, expensive and often inaccurate process. As recycling efforts in communities increase, so does the need for a faster and more efficient recycling sorting method.
Further, the use of new plastic resins has placed greater demands on the correct identification and sorting of the various types of materials used to produce plastic containers. One such new resin is polyethylene naphthalene (PEN). This resin has superior shelf life and temperature tolerances, but must be identified, sorted, and recycled apart from other plastic resins. Although PEN is similar to other widely used and recycled polyesters such as polyethylene terephthalate (PET) and various grades such as PET-G, PEN must be detected and sorted separately so that processing problems are avoided and the recyclate has satisfactory properties.
Various arrangements have been proposed for sorting recycled materials and are as follows:
U.S. Pat. No. 4,919,534 to Reed sorts returned glass and PET bottles by testing the material with polarized and colored light. Alternately flashing red and green polarized light is optically detected as the light passes through the bottle. The rotation of the polarized light differentiates between glass and PET. PA1 U.S. Pat. No. 4,858,768 to Plester removes plastic bottles which have been contaminated prior to their arrival at the sorting center. Warm water is injected into the plastic bottle, agitated, and various residue analyzers determine the characteristics of the residue. For example, electromagnetic radiation, light scattering, polarized light rotation, and X-ray fluorescence may be used to examine the residue. PA1 U.S. Pat. No. 4,248,389 to Thompson et al. discloses a detector which sorts recycled bottles by scanning the Universal Product Code (UPC), using that code to classify the bottle, and sorting the bottle into the appropriate bin for later reclamation. PA1 U.S. Pat. No. 3,358,552 to Schneider discloses sorting bottles by optically determining the placement of a label, the color of the bottle, and the pattern engraved in the glass. The outlets of these sensors are fed into a logic circuit, which then determines the commercial affiliation of the bottle by determining the combination of the triggered detectors. PA1 U.S. Pat. No. 4,848,590 to Kelly discloses sorting different types of scrap metal on the basis of their X-ray fluorescence. Depending on the type of metal detected, the metal is directed to various storage areas. PA1 Japanese Patent No. 56145339 generally discloses detecting chlorine in a vinyl chloride resin to determine the degree of aging of the resin. PA1 U.S. Pat. No. 5,024,335 to Lundell discloses a mechanical sorter for removing large plastic containers and aluminum cans from other refuse. A variety of refuse is transported below rotating brushes. Those containers which are too large to fit under the brushes are lifted off the conveyors and over the top of the brushes. After the containers pass over the top of the brushes, they are diverted to a separate conveyor for later removal.
Despite all the effort toward the development of recycling methods and apparatus, further improvement is needed. Furthermore, existing detection and sorting equipment are required to detect new types of packaging resins. This invention meets these needs.